Yes Bill, PRS-10 is quite the amazing item. Sorry to hear about the battery expense, is it just the custom size that causes the issue? Interesting you get slightly better ADEV using them. The STA-61 has a battery option, but mine does not have it.
I did an experimental ADEV 8 hour run using the tester's (PRS-10) timebase... looped it on a short coax to the test input. It was even better results than the standalone PRS-10 I have... Not sure if this is a valid test or not, but I think so.